When we think of bridges, it is the dramatic and monumental long spans that come to mind first, especially the lithe suspension bridges such as the Golden Gate and the pure geometric arches such as Sydney Harbour. But the majority of bridges are not such spectacular structures. Most of them are ordinary overpasses, with spans of 30 or 40 feet, carrying roadways or rails across other thoroughfares or over small streams. You see such bridges by the dozen on any drive down the Interstate. They may be lacking in glamour, but they are more representative of a bridge builder's art.
The engineering and construction of girder bridges are pretty routine these days, but the bridges are not quite standard items you order from a catalogue. The girders, whether of steel or concrete, are custom-build for each bridge, then trucked to the site and hoisted into place with a crane. The designer still has scope for variation and creativity, and it shows out on the highways: some overpasses are prettier than others.
"There's a consistency to physical objects that somehow reads all the way through, so that when you make a physical object, if it lacks the proper amount of weight or if it lacks a certain density...I mean, if its outside says, 'I weigh so much and I have such-and-such a density,' and when you pick it up, you discover an inconsistency there, then you can sense that, you can see it, even without picking it up. It's absolutely essential that everything be done all the way through."